Field of the Invention
The invention relates to a system for monitoring data from vehicle tires, for example a tire pressure monitoring system and more particularly a method for determining the position (on the vehicle) of a tire having a unique identification number (ID). This tire position can be each of the following positions: front left (FL), front right (FR), rear left (RL), rear right (RR).
Description of the Related Art
Known tire pressure monitoring systems (TPMS) comprise a wheel unit installed in each wheel, a reception antenna on the vehicle, and a central processing unit fitted to the vehicle to monitor the pressures of the tires. Each wheel unit comprises a transmitter to transfer the data from sensors installed in the wheel units. Said sensors can be chosen from a group comprising: a pressure sensor which measures the internal air pressure of the tire, a temperature sensor which measures the temperature of the air inside the tire, an angular position sensor, an accelerometer, etc. Other sensors can be present in the wheel unit to detect faults or to measure other parametric values associated with the tires or wheels. To each wheel unit, there is assigned a unique identifier ID transmitted via radio with data measured by this sensor to the vehicle reception antenna of the vehicle, then to the vehicle central processing.
The identifier (ID) is initially memorized in the central processing unit, and associated with the position of the corresponding wheel. The central processing unit can generate information relating to the tires or alert messages intended to be displayed for the driver, for example in the case of low tire pressure. If a vehicle remains motionless for a relatively long duration, the assignment of the identifier ID to a position on the vehicle is restarted since one or more tires may have changed place or the tires may have been inverted while the vehicle was immobile.
Certain known tire pressure monitoring systems can perform position assignment (locating) of respective air pressure sensors automatically, i.e. without specific actions by the driver. In a known process, each wheel housing is equipped with a triggering unit. Each triggering unit successively transmits an activation signal. The wheel units successively respond to the triggering units, thus learning their identifier ID and determining their position simultaneously. These methods, which explicitly implement the initialization process (recognition of identifiers related to the vehicle) and the locating process in a single step are generally associated with increased component costs and with a relatively overall system high degree of complexity.
With a reduced number of components, the method is carried out in two stages. In the first stage, generally called the “initialization” stage, the vehicle identifiers are collected. In the second stage, a wheel position is assigned to each collected identifier. The second stage is generally called the “locating” stage.
The initialization function is mainly based on statistical steps. An increasing number of vehicles are equipped with tire pressure monitoring systems. However, the number of radio frequencies is limited. Thus, it can arise that when one vehicle moves close to another, the receiver of one of the vehicles receives the identifiers from the other vehicle wheels. The initialization function is based on the assumption that the transmissions of identifiers of correct vehicle wheel units are received more frequently than the neighboring vehicle identifiers. Once the identifiers are collected, the accuracy of the result can be assessed and robustness improved by evaluating additional information.
For example, all the wheel units of the same vehicle should have substantially the same rotation speeds (if the vehicle moves in a straight line at a steady speed) and approximately similar temperature profiles. It is also possible to assess the intensities of the received signals. However, the described approaches can lead to false conclusions or to no conclusion at all if two or more vehicles move one beside the other or one behind the other for a relatively long period of time. This can arise when the vehicle is in heavy traffic conditions.
The locating of new tire positions, carried out after each relatively long stoppage of the vehicle, has the main drawback of the tire pressure monitoring system being occupied for a relatively long time for the correct assigning of identifiers and of wheel units corresponding positions, before the system can evaluate the measured air pressures in the normal operating mode and assign them to a corresponding wheel unit position on the vehicle. Hence, the driver, in the event that the air pressure in a specific tire falls, may be warned late.
Often, the vehicle has already left a parking spot when a pressure alert message is displayed. The driver must then stop the vehicle at an awkward place or drive for a longer time with an incorrect air pressure before being able to solve the tire problem. Either case constitutes a real safety risk.